As the number of cellular subscribers in a metropolitan area increase, the number of switching nodes in the area increase. The work that the wireless communications network must do to track the movement of mobile subscribers between switching nodes is more than the work required to track subscriber movement within one single switching node. In a GSM network for example, part of the work that must be done when a mobile subscriber moves to a new switching node is Authentication. Authentication is the process by which a mobile switching center (MSC) ensures that the mobile subscriber is really a valid user. In order to authenticate the mobile subscriber, a set of authentication triplets is required from a home location register HLR. Conventionally, the MSC uses one of these sets of authentication triplets each time the mobile subscriber is authenticated, and then throws away this triplet (GSM specification recommendation).
Referring to FIG. 1, there is shown a conventional wireless communication system 10, which may be a GSM, TDMA, CDMA etc. technology. The gateway MSC12 communicates calls between a public switched communication network (PSTN) 14 and a plurality of base switching center (BSCs) 16. The BSCs 16 in turn, service the mobile subscribers (MSs) 18 via RF radio signals. Each MSC 12 has a visitors location register (VLR) 22 for storing currently served MS 18 information. The amount of work the MSC 12 spends on requesting authentication triplets from the home location register of the serviced mobile subscribers (HLR) 20 is significant. Moreover, the amount of work the HLR 20 spends generating these authentication triplets is higher than the work done by the MSC 12. As the rate of the mobile subscriber moving between switching nodes increases i.e. BSC to BSC for a different MSC, which is commonly referred to as inter-VLR location update, the amount of Authentication increases. This may result in more Authentication occurring in the network 10 than the cellular service provider intends. This increase in Authentication causes a decrease in the number of mobile subscribers 18 that each node (MSC 12) in the network can support since extra work (i.e. extra CPU processing) must be done for Authentication.
In the past, to increase the capacity of the MSC 12, many different mechanisms have been used. These include hardware upgrades to faster processors, software optimizations, and the reduction of the amount of work required to be done by the MSC 12 e.g. by reducing messaging for inter-VLR location updates such as disclosed in commonly assigned U.S. patent application Ser. No. 08/864,927, entitled "Distributed Subscriber Data Management in Wireless Network" filed May 29, 1997, and U.S. patent application Ser. No. 08/864,926, entitled "Distributed Subscriber Data Management in Wireless Networks from a Central Perspective" filed May 29, 1997, the teachings of which are included herein by reference.
Authentication can occur on the following events: call originations, call terminations, inter-VLR location updates, intra-VLR location updates, and periodic location updates. The frequency of authentication is specified via an operator controlled parameter (except for inter-VLR location updates, which must always be authenticated). Presently, the MSC/VLR can store N authentication triples per mobile subscriber. One triplet is used each time an authentication event occurs. The triplet that was last used to authenticate the subscriber is marked as the "current triplet".
When an authentication event has been completed, the MSC/VLR currently serving the mobile subscriber checks to see how many triplets are left for that subscriber. If there are X number of triplets left, the MSC requests more triplets from the subscribers HLR. The HLR then generates up to 5 triplets and sends them to the MSC.
Currently, the rate that authentication triplets are requested from the HLR is in direct proportion to the number of events that are occurring on the MSC. The rate is especially sensitive to the number of inter-VLR location updates that are occurring which especially high for a High Mobility MSC that serves a metropolitan area. The relationship between events and Authentication triplet requests is graphed in FIG. 2. The lines represent the ratio of Events to Triplet Requests for a Low Mobility MSC and a High Mobility MSC.
There is a desire for an improved method to reduce the number of requests to the HLR for Authentication triplets in a wireless communications network to achieve a capacity increase on the MSC and a capacity increase on the HLR. This increases the number of subscribers that may be supported by each MSC.